Electrical distributor



26; 1944. E. ZQERLEW ETA; 2,365,925

ELECTRI CAL DI STRIBU'IOR Filed June 2. 1942 4 Jo}: E y John H. MickeyIii/5) Z INVENTORS. By 654%. 22 5.

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ATTOJPNEYS.

Patented Dec. 26, 1944 ELECTRICAL DISTRIBUTOR Emil Zoerlein, John L.McCloud, and John A. Mickey, Dearborn, Mich., assignors to Ford Mo torCompany, Dearborn, Miclr, a corporation of Delaware Application June 2,1942, Serial No. 445,462

Claims.

The object of our invention is to provide an internal-combustion enginedistributor by means of which high-tension current is selectivelyconducted to the several spark plugs associated with such engine. Ourinvention comprises an improved distributor-cap construction in that ourcap has an increased dielectric strength over other caps of similarsize.

Our invention is particularly useful in aircraft engine distributorsbecause the ceiling of most airplane engines is determined by theminimum atmospheric pressure at which the distributor will handle thecurrent required for ignition. The use of superchargers andpressure-sealed fuselages has increased the ceiling of planes to such anextent that failure of the distributor is the controlling factor. Due tothe increased dielectric strength of our cap, the distributor willfunction at nearly 10 per cent higher altitudes than was heretoforepossible.

In the modern airoraftengine a potential of 9,000 to 14,000 volt isrequired for ignition, due to the high compression pressures.Substantially this same voltage is required up to 30,000 feet becausethe supercharger of the engine maintains almost a constant compressionpressure up to this height. However, at these altitudes the atmosphericpressure inside the distributor cap is so low that the danger ofshorting around the plugs is of major importance. The ordinarydistributor cap is made from either rubber or phenol condensate and areduction in barometric pressure reduces both the surface dielectricstrength and the volume dielectric strength of the cap. The surfacestrength is reduced because it is directly proportional to theatmospheric pressure, while the volume dielectric strength is reducedbecause the material is porous to a slight degree.

A further factor in connection with such distributors is that nitricacid is formed in the atmosphere within the housing due to thecontinuous sparking between the rotor and the spark plug wire terminals.The acid accumulates upon the walls of the housing and wets the surface,thereby reducing the surface dielectric strength.

We have improved the dielectric strength of our distributor cap byproviding a laminar construction, one element of which seals the poresof the cap material, provides an acid-repellent surface for the interiorof the cap, and is of such composition that an unexpected increase involume dielectric strength results.

With these and other objects in View, our invention consists in thearrangement, construction and combination of the various elementscomprising our improved distributor and the method of accomplishing theresults attained, as described in the specification, claimed in ourclaims, and illustrated in the accompanying drawing, in which:

Figure 1 is a plan view of an airplane engine distributor cap, and

Figure 2 is a cross-sectional view, taken upon the line 2-2 of Figure 1.

Referring to the accompanying drawing, we have used the referencenumeral ID to indicate a housing which is molded of mica-impregnatedphenol condensate. Hard rubber or other similar material may, however,be used if desired. The housing is of cup shape having a centralterminal II molded therein, which terminal is electrically connected toa threaded eyelet l2 by means of a wire l3. The terminal ll, eyelet I2and wire I 3 form a unit which is molded in the housing 10. High-tensioncurrent is conducted from the magneto coil to the eyelet H by means of acable which is inserted in a socket M in the housing. A screw, notshown, is screwed into the eyelet and contacts a ferrule on the end ofthe cable. The current from the terminal H is conducted to individualspark-plug terminals 15 by means of a conventional distributor rotorwhich is not shown in the drawing. One terminal [5 is provided for eachspark plug of the engine, each of which terminals is connected to aneyelet I6 by means of a wire ll. The terminals 15 are arranged in anannulus around the periphery of the housing [0.

Where the engine is provided with upward of eighteen cylinders, acomparatively large distributor cap is required, solely to obtain thenecessary annular spacing between the terminals ii. In order to decreasethis spacing the surface path between the adjacent connectors 16 iselongated by providing radially extending ribs I8. The spacing of theterminals I5 and height of the ribs l8 control the dielectric strengthof the housing and are chosen so that at atmospheric pressure thehousing will safely carry a potential of 16,000 volts.

Our distributor differs from the conventional distributor in that theinside of the housing In is coated with a special enamel. Furthermore,

the inserted portions of the terminals II and I5, eyelets l2 and theconnecting wires [3 and H are coated with this enamel before they aremolded in place. The action of these coatings is not exactly clear tothe applicants but the results attained are far superior to those whichcould be expected from the actual insulating value of the enamelemployed. The improvement may be because the layer of enamel forms awater-impregnable surface, sealing the pores in the housing surface, orit may be becaus the coating is acid repellent, thus being unaffected bythe dilute nitric acid formed by the arcs at the several terminalswithin the housing.

In any event the coating which we appiy is only about .010 inch thickbut it increases both the surface and volume dielectric strengthsuiiiciently that the housing withstands over 2,000 additional volts.This increase is entirely out of proportion to the increase that mightbe expected from the additional .010 inch of dielectric.

The enamel which we have found desirable consists of a resin mixture of75 per cent alkyd and 25 per cent melamine resins and from to per centpigment based on the amount of resin.

Such enamel will bake at 175 to 200 degrees, these temperatures beinglow enough not to warp the housing. The thickness of the coating is notof particular importance, as apparently the increase in dielectricstrength does not depend upon the actual thickness of the coating. Itshould, however, be of sufficient thickness to completely cover thesurface. The pigment may be any one of several but should be heatresistant and free from iron oxide. Any of the various silica compoundsare suitable for this use.

Some changes may be made in the composition of the above-describedcoating and the parts to which it is applied without departing from thespirit of our invention, and it is our intention to cover by our claimssuch changes as may reasonably be included within the scope thereof.

We claim as our invention:

1. An ignition distributor housing comprising melamine as a componentpart of the surface thereof.

2. A distributor housing comprising dielectric material, the surface ofwhichis provided with melamine resin.

3. A distributor housing comprising dielectric material and a layer ofmelamine applied thereto.

4. The structure, as defined in claim 3, in which the melamine resin ispresent as a film applied to said dielectric material.

5. In a distributor of the class described, a distributor body moldedfrom a. phenolic resin and a mica filler, said body forming an enclosurefor a high tension electric spark, the interior or said distributorhaving a thin dielectric layer of finely divided silica material in amedium comprising a thermosetting alkyd resin'and a thermosettingmelamine resin cured in situ on said body, there being a substantialexcess of said alkyd over said melamine resin.

6. In a distributor molded from dielectric material, a compartmentforming an enclosure for a high tension electric spark, the interior ofsaid compartment having a thin enamel coating applied thereto, theessential ingredient of said enamel being melamine resin.

'7. In a distributor of the class described, a distributor head moldedfrom a slightly porous insulating material, and a conductor having athin enamel coating thereon, the essential ingredients of said enamelincluding alkyd and melamine resins, said conductor being imbeddedwithin said head.

8. In a distributor of the class described, a distributor head moldedfrom a phenolic resin insulating material, an enamel-coated conductorpartially imbedded within said head, and a layer of enamed formed on theinterior surface of said head, the essential ingredient of said enamelsincluding alkyd and melamine resins.

9. In a distributor of the class described, a distributor head moldedfrom mica-impregnated phenolic resin, said head forming an enclosure fora high-tension spark, the interior of said enclosure havin a pigmentedenamel coating applied thereto, the essential ingredients of said enamelcomprising alkyd and melamine resins and a heat-resistant pigment freefrom iron oxide.

10. In an electric distributor of th class described, a distributor headmolded from micaimpregnated phenolic resin, said head forming anenclosure for a high-tension electric spark, the interior walls of saidenclosure having a layer of enamel formed thereon, and an enamel-coatedconductor imbedded within said head, said enamels comprising alkyd andmelamine resins and a silica pigment.

EMIL ZOERLEIN. JOHN L. MCCLOUD. JOHN A. MICKEY.

